As viewed from above in the schematic plan view of FIG. 1, a prior art steam generating plant may include multiple steam generators 10 arranged side-by-side. In the illustrated example, each steam generator 10 has a once-through water line 12. The water line 12 at each steam generator 10 has an inlet 14 for receiving a stream of liquid water, and has an outlet 16 for discharging a two-phase mixture of steam and liquid water. The output of the steam generators 10 may be used in processes such as, for example, the enhanced recovery of oil. The water lines 12 at the multiple steam generators 10 may share a common source 17 and one or more process locations 18.
Each steam generator 10 in the illustrated example further has a burner 20, a radiant heating portion 22, and a convective heating portion 24. The radiant heating portion 22 defines an upstream heat exchange chamber 25 with a cylindrical shape. The convective heating portion 24 defines a downstream heat exchange chamber 27 with a generally rectangular shape. The burner 20 fires into the upstream chamber 25. A port 29 communicates the upstream chamber 25 with the downstream chamber 27.
The respective water line 12 at each steam generator 10 first reaches into the downstream chamber 27. Typically, the water line 12 reaches through the downstream chamber 27 along a serpentine path in a stack-like arrangement of parallel sections 30. For example, a single section 30 of the water line 12 is shown in the top view of FIG. 1. Like the other sections 30, this individual section 30 reaches lengthwise in horizontal directions that alternate back and forth across the chamber 27, with multiple horizontal turns 32 of 180 degrees. As shown in the side view of FIG. 2, the multiple horizontal sections 30 of the water line 12 are interconnected by vertical turns 34, with each vertical turn 34 reaching from one horizontal section 30 to the next.
The water line 12 emerges from the downstream chamber 27, and then continues into and through the upstream chamber 25 along another serpentine path before reaching the outlet 16. However, the water line 12 does not reach significantly across the upstream chamber 25, but instead reaches primarily along the periphery of the upstream chamber 25. Specifically, horizontally elongated sections 40 of the water line 12 reach oppositely back and forth along the length of the chamber 25 at its periphery, with turns 42 that interconnect the sections 40 in an array reaching circumferentially around the chamber 25.
The interconnected sections 30 and 40 of each once-through water line 12 are thus arranged in series as heat exchange tubing within the two chambers 25 and 27 in the respective steam generator 10. In operation of the steam generator 10, the respective burner 20 provides gaseous products of combustion that flow through the chambers 25 and 27 and further outward through a stack 50. As the products of combustion flow through the downstream chamber 27, they flow around and against the water line sections 30 that reach across that chamber 27, which results in convective heating of the water flowing through those water line sections 30. The water that is preheated in this manner in the downstream chamber 27 next flows through the water line sections 40 in the upstream chamber 25, where it is further heated radiantly by the products of combustion flowing through the cylindrical space surrounded by those water line sections 40. The two-phase mixture of steam and liquid water is then discharged from the outlet 16.